[#BloombergLP-bslfmt-FormatterSpecificationNumericValue_ArgVisitor-operator_call-0e]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bslfmt.adoc[bslfmt]::xref:BloombergLP/bslfmt/FormatterSpecificationNumericValue_ArgVisitor.adoc[FormatterSpecificationNumericValue_ArgVisitor]::operator()
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:mrdocs:

Throw `format_error` when visiting an empty format argument.

== Synopsis

Declared in `<bslfmt_formatterspecificationnumericvalue.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
void
operator()(std::monostate value) const;
----

== Description

This indicates visitation of an argument with no value, which would indicate a logic error. Note that this would only be called when extracting a value from a `basic_format_arg` that holds no value, which would normally indicate an incorrect argument type.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *value*
| empty monostate argument (unused)
|===


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